Then they shouldn't have written that. Or the rules for lances should not be as they are. The two are mutually exclusive.
Sorry. 40k is full of things that are mutually exclusive, I've found.
No, they don't match up. You don't see orbital strikes in 40k with a 100m radius. Obviously what is an orbital strike in fluff is significantly different from what constitutes an orbital strike in game.
That's because there are only two blast templates in 40k, and it's obviously not going to be the small one. Also, Space Marines are individually capable of killing an entire 1500 point IG force in fluff, so I just think of it being nerfed to scale. IIRC in Apoc they use the XL blast template instead, which is about 100m.
No, every weapon can be used against ships. Against mobile targets weapons fare worse. Bombardment cannon fare worse. Even torps fare worse. Lances however, do not fare worse. In fact, they fare worse than the alternatives against stationary targets. The only point to taking them in place of the other weapon systems is to use specifically against ships.
Or against precise targets on the ground, given their much smaller area of mass destruction compared to Weapon batteries. 1km vs 10-20km of damage. The area that armor and cover saves do not apply is fairly small with a lance. Here's what seems to be eluding you. Marines are surgical strike experts. A Bombardment canon deals damage comparable to a nuke, demolishing things for 20km. A lance more comparable to a MOAB, but with better armor penetration on the target. Which is better for close support?
No one is less trustworthy than SMs. This is because they are more powerful than anyone else. They are far far harder to control. And when they rebel they are far harder to put down and are far more likely to be able to exert influence over Imperial forces. If you throw on top of that no restrictions on their fleets then they are for all intents and purposes uncontrollable.
Wait... Space Marines are less trustworthy then Rogue Traders? The paragons of humanity's defenders are less trustworthy then a group that sells out the Imperium on a regular basis, and has, on occasion, destroyed entire Sectors or successfully led them in rebellion against the Imperium. That head up the Inquisitions list of 'the usual Suspects' hot on the heels of Xenos and the Ruinous Powers? That finance and occasionally lead the Crusades that the Imperium uses to conquer sectors. Those guys?
Virus bombs and Nova cannon are meaningless in the hands of people easily conquered, assassinated or controlled.
Assassinating a Rogue Trader is not easy. A lord Sector would actually be simpler. The reason is that it's hard to know where one might turn up next, and most of them are highly paranoid about just that, having survived their own siblings attempts to eliminate them during their rise to power. Considering that Rogue Traders recruit their assassins from the same Death Cults that the Inquisition does, and may, in fact, have their own private death cult on board their ship on the look out for other assassins... well...
The other option is to deploy a navy task force to hunt a rogue trader, but this can also prove difficult. Rogue Traders spend much of their time in areas with little or no Imperial presence to report intelligence on their movements. More frightening, on occasions, IN task forces sent to eliminate a rogue trader have been destroyed, vanished, or worst, been taken by said rogue trader and added to their private fleet.
What? Of course the traitor legions are a threat. It's absurd to think otherwise. As for the "oh noes, we're outnumbered" idea, they're Space Marines, they're used to fighting against superior numbers. In fact, they're expected to. Also, that overwhelming Imperial Navy is spread out all over the galaxy. If SMs are no threat at all to the Imperium then they're also no use to it. They're numbers are too insignificant to make them worth mentioning. Delete the fleet.
The fact is that that the Imperium wants is to be able to soundly defeat any SM fleet on a 1 for 1 basis. Not on a 2000 to 1 basis. It is natural for Imperial commanders to grow concerned over any steps by the SM in the direction of battlefleet. This includes putting lances on ships.
Well, one, most SM fleets are also spread throughout the Imperium. The 'SM fleet' as exists in BFG would be an average chapter amassing their entire fleet in one spot. Which in fluff is nearly unheard of. Most commonly, one or two strike cruisers might be gathered together. Granted, there are chapters such as the Black Templars or Space Wolves which have much larger fleets, but the Armada SM fleet is an anomaly. The Crusade and Dominion fleets make sense in the context of fluff, though Crusade might have some lances, and Dominion should DEFINITELY have 'real' lances, as they are doing the job that normally is preformed BY IN, in regions that IN has no jurisdiction.
OT: as far as 'than' and 'then' when typing on forums or in reviews, I tend to type in the same manner I speak. This does include such verbal oddities as misusing 'than', as in the region I hail from, 'than' and 'then' sound pretty much the same when spoken. You should count yourself fortunate that I mentally edit out such other peculiarities as 'dan tan' for 'down town' and 'warsh' for 'wash'. I hesitate to imagine your suffering in an area where one might be asked to 'red up' or go watch the 'Stellers' play across the 'Mon' while downing an 'imp and arn'.